As some of you may already be aware, we have begun construction of a new forum as a rebirth of PHO and continuing on into future projects.
This forum is called Silph Co., and can be found by clicking the banner below. We are in the process of transferring some of our old resources, and the forum is open for posting. It will be sad to see PHO go, but we look forward to a bright future with Silph.
The forums here will be moved to an archive, and the url will redirect to the new site in the coming days/weeks.

The difference between FireRed and Emerald is that the Emerald's table only covers 10 backgrounds which are in this list:

Grass 1 (Normal Grass)

Grass 2 (Tall Grass)

Sand

Dive

Sea

Pond

Craggy

Cave

Trainer Battles (Indoor)

Trainer Battles (Outdoor) "can be called as the outdoor FIELD"

The table begins at 31ABA8 and ends at 31AC6F. The table hasn't the background for Gym Leader battles, Hideout battles, Pokemon League battles, Battle Frontier battles (doesn't count the Smeargle cave underneath Battle Frontier), and the backgrounds for the Weather Trio battles isn't in the table too. I'm pretty sure that the table is somewhere else but they are located separatedly. Here is the documentation of each background and their offsets and pointers in the original table:

So far, that's only the separated backgrounds I've found in Emerald. Some of the images are aligned with the first ten backgrounds or the other backgrounds so be careful while repointing. Example: You have a background for the Elite Four and Champion but it relates with the Team Rocket Style background. I suggest that if you have good instincts, insert the image without repointing and just edit the pointers manually by using a HEX editor. I just gave all the information I have found so you won't be having problems dealing with Emerald background. I hope this help you a lot. Good luck!